When information bits are encoded by a systematic channel coder, redundancy bits are added to the information bits. An example of the systematic encoder is a convolutional turbo code (CTC).
Quadrature amplitude modulation (QAM) from among the modulation methods converts a plurality of bits of transmission data into phase and amplitude information of a symbol and transmits the same. 16-QAM can transmit 4 bits with a symbol, and 64-QAM can transmit 6 bits with a symbol.
The 16-QAM is a method for dividing the data to be transmitted into 4-bit units, mapping each of the units to one of 16 symbols, modulating them, and transmitting them, and it generally uses the gray mapping for the symbol mapping method. When the 4-bit symbol that is modulated by the gray mapping is received, the bits of the received symbol respectively have different reliability. For example, the reliability of the received bits can be shown as log likelihood ratio (LLR) values.
Since the related art maps the symbol without distinguishing reliability differences, information bits, and redundancy bits, a block error rate (BLER) is high.
In addition, a wireless communication system uses a retransmission scheme to improve the performance. According to retransmission scheme, when a receiver fails to receive a packet correctly, the packet is retransmitted. A hybrid automatic retransmit request (HARQ) scheme is one example of the retransmission scheme. In the retransmission scheme, the reliability of the bits may be an important factor to reduce the BLER of the packet.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.